Having established the fundamental principles of ETL in the previous chapter, we now focus on the first stage: Extraction. This is where the process begins, retrieving raw data from its originating systems.

This chapter covers the practical aspects of getting data out. You will learn about:

• Connecting to diverse data sources, such as databases, files, and APIs.
• Different strategies for data retrieval, including full versus incremental extraction.
• Techniques for handling structured data (like tables) and semi-structured data (like JSON or XML).
• An introduction to Change Data Capture (CDC) for efficient tracking of data modifications.
• Common challenges encountered during extraction and basic error handling.

By the end of this chapter, you will understand the methods and considerations involved in successfully extracting data as the initial step in building an ETL pipeline.